TWIST AND Msx2 IN BOUNDARY FORMATION AND CRANIOSYNOSTOSIS

边界形成和颅缝闭合中的扭曲和 Msx2

• 批准号: 6988417
• 负责人: Robert E. Maxson
• 金额: $ 40.65万
• 依托单位: UNIVERSITY OF SOUTHERN CALIFORNIA
• 依托单位国家: 美国
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-08-01 至 2010-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6988417
• 关键词: biological signal transduction; bone morphogenetic proteins; craniosynostosis; gene expression; laboratory mouse; mutant; phenotype; protein protein interaction

DESCRIPTION (provided by applicant): This is a proposal to investigate the morphogenesis of the coronal suture and mechanisms of coronal synostosis. The long-term aim is to understand how boundaries between cellular compartments form, and how such boundaries function in growth control and patterning. The cellular mechanisms underlying craniosynostosis are largely unknown. Prevalent views, based largely on ex vivo approaches, seek to explain craniosynostosis in terms of the timing of differentiation or survival of osteoblast populations. Our results suggest that understanding the fundamental causes of craniosynostosis requires an analysis at a higher level of biological organization. Through an examination of the Twist mutant mouse, we found that synostosis of the coronal suture is associated with a defect in the boundary between neural crest-derived mesenchyme that forms the frontal bone and mesodermal-derived mesenchyme that forms the parietal bone. In an effort to identify other genes that function together with Twist in coronal suture development, we have uncovered evidence that perturbations in Eph-ephrin and Bmp signaling may contribute to these defects. That ephrin signaling may have a part in the Twist mutant phenotype is suggested by our observations (i) that ephrins A2 and A4, as well as their receptor, EphA4, are expressed in a highly localized manner in the developing coronal suture, (ii) and that their expression is altered in Twist mutant mice and restored to their wild type pattern in Msx2-Twist double mutants. That BMP signaling is involved is suggested by our observation that the gene encoding the Bmp antagonist, noggin, is upregulated in the prospective coronal suture of Twist mutant mice, and that transgenic overexpression of noggin causes a sutural defect similar to that seen in Twist mutants. Moreover, inactivation of Bmp4 in neural crest also causes fusion of the frontal and parietal bones at the coronal suture. These data lead us to the hypothesis that craniosynostosis in the Twist mutant is caused in part by a perturbations in gene networks that control boundary formation, and that these networks are likely to include elements of the Eph-ephrin and BMP pathways. Here we propose (i) to carry out a series of genetic experiments aimed at testing the hypothesis that Twist interacts functionally with the Eph-ephrin and BMP pathways in the patterning of the coronal suture; (ii) to test the hypothesis that Msx2 and Twist function cooperatively in a genetic cascade that regulates boundary formation and coronal suture development. This will entail an analysis both of coronal suture development and the expression of ephrinA2 and EphA4 in Msx2-Twist double mutants. Finally, we will examine the regulatory relationship between Msx2 and Twist. We will investigate the mechanism by which reduced Twist function leads to expanded expression of Msx2, and we will determine whether upregulation of Msx2 is sufficient to cause a boundary defect and synostosis in the coronal suture. The significance of the proposed studies is, first, that they will contribute information on the pathophysiology of an important class of craniofacial disorders-the craniosynostoses. Second, they will address the biological significance of boundary formation in patterning and growth control-a fundamental problem in developmental biology.

描述（由申请人提供）：这是一项研究冠状缝形态发生和冠状缝骨连接机制的提案。长期目标是了解细胞区室之间的边界如何形成，以及这些边界如何在生长控制和模式化中发挥作用。颅缝早闭的细胞机制很大程度上是未知的。主要基于离体方法的流行观点试图用成骨细胞群体的分化或存活时间来解释颅缝早闭。我们的结果表明，了解颅缝早闭的根本原因需要在更高水平的生物组织上进行分析。通过对 Twist 突变小鼠的检查，我们发现冠状缝的骨连接与形成额骨的神经嵴衍生的间质和形成顶骨的中胚层衍生的间质之间的边界缺陷有关。为了确定在冠状缝发育中与 Twist 一起发挥作用的其他基因，我们发现了证据表明 Eph-ephrin 和 Bmp 信号传导的扰动可能导致这些缺陷。我们的观察表明，肝配蛋白信号传导可能在 Twist 突变表型中发挥作用（i）肝配蛋白 A2 和 A4 及其受体 EphA4 在发育中的冠状缝中以高度局部化的方式表达，（ii）它们的表达在 Twist 突变小鼠中发生改变，并在 Msx2-Twist 双突变体中恢复到其野生型模式。我们观察到，编码 Bmp 拮抗剂 noggin 的基因在 Twist 突变小鼠的预期冠状缝中表达上调，并且 noggin 的转基因过度表达会导致与 Twist 突变体中相似的缝线缺陷，这表明 BMP 信号传导参与其中。此外，神经嵴中 Bmp4 的失活还会导致额骨和顶骨在冠状缝处融合。这些数据使我们得出这样的假设：Twist 突变体中的颅缝早闭部分是由控制边界形成的基因网络的扰动引起的，并且这些网络可能包括 Eph-ephrin 和 BMP 途径的元素。在此，我们建议 (i) 进行一系列基因实验，旨在检验 Twist 在冠状缝图案化中与 Eph-ephrin 和 BMP 通路功能性相互作用的假设； (ii) 检验 Msx2 和 Twist 在调节边界形成和冠状缝发育的遗传级联中协同发挥作用的假设。这将需要分析 Msx2-Twist 双突变体中的冠状缝发育以及 ephrinA2 和 EphA4 的表达。最后，我们将研究 Msx2 和 Twist 之间的监管关系。我们将研究 Twist 功能减少导致 Msx2 表达扩大的机制，并将确定 Msx2 的上调是否足以引起冠状缝的边界缺损和骨性连接。拟议研究的意义首先在于，它们将为一类重要的颅面疾病——颅缝早闭的病理生理学提供信息。其次，他们将解决边界形成在模式和生长控制中的生物学意义——发育生物学的一个基本问题。